1. Field of Invention
This invention relates to an improved air exhaust system, which can be utilized in the field of building and vehicle ventilation, as well as in the field of roof construction for creating suction or negative pressure underneath a membrane or other roof materials against wind uplift.
2. Discussion of Prior Art
Roof components and materials are susceptible to uplift damage caused by strong winds. U.S. Pat. Nos. 4,223,486; 4,557,081 and 4,888,930 to T. L. Kelly, Waterbury, Conn. taught a method to equalize or balance the uplift on the upper surface of the membrane by channeling the negative pressure therein to underneath the membrane.
That method, while intended to tap the negative pressures that occur in the roof corner and edge areas, has the potential to actually feed positive pressure into underneath the membrane, enhancing the uplift force so as to worsen the situation. This is because of the fact that the wind flow on the roof is highly turbulent and complex, frequently deviating from the situation the Kelly equalizer system is designed for. Particularly in the roof corner and edge areas the airflow is dominated by strong, fluctuating and intermittent vortices, and pressures therein fluctuate significantly from negatives to positives as evidenced in wind tunnel and field test data. Strong down-wash flow also occurs frequently due to the effects of the edge/corner vortices or the influences of adjacent taller structures, which creates positive pressure, potentially on the parts of the roof where the Kelly system unit is installed. Although the Kelly method also includes a valve intended to “prevent” any positive pressures from entering into underneath the membrane, the air tightness of the contracted valve sleeves is hardly sufficient to block out the infiltration of positive pressures. Such additional mechanism also complicates the system, increases the probability or chances of component and system failure, and raises the cost of the system as well.
In the field of building and vehicle ventilation, a number of designs exist for aiding air exhaust or air relief, for example, U.S. Pat. Nos. 6,582,291 B2; 6,302,778 B1; 5,326,313; 4,379,972; 4,086,028 and 3,952,638 to various inventors. However, none provides a simple and effective method. Most of them involve complicated and expensive moving parts such as turbines, fans and associated bearings etc., which also increase the chances of mechanical failure.